Control rod canopy seal positioning and welding system

ABSTRACT

A remotely controlled robotic welding arm is provided that is designed to service the omega seal site between the control rod drive mechanism and adapter tube of a nuclear reactor stalk head and is specifically concerned with welding the canopy seal to contain radioactive steam released in the event of an omega seal failure.

This is a division of application Ser. No. 07/376,512 filed Jul. 7,1989, now U.S. Pat. No. 5,031,816.

BACKGROUND OF THE INVENTION

This invention generally relates to the servicing of the omega seal sitewhere a control rod drive mechanism attaches to the adapter tube of anuclear reactor head stalk, and is specifically concerned with welding acanopy seal about the omega seal site to contain the radioactive steamreleased in the event of an omega seal failure.

The core of a modern nuclear reactor of the type used to generateelectrical power generally includes an upper internals assembly disposedover a lower core barrel. The lower core barrel houses an array of fuelrod assemblies which generate heat as a result of a controlled fissionreaction that occurs in the uranium oxide pellets present in theindividual fuel rods. Water is constantly circulated from the lower corebarrel through the upper internals and out through outlet nozzlesprovided in the walls of an upper core barrel in order to transfer theheat generated by the fuel rod assemblies to heat exchangers whichultimately convert this heat into usable, nonradioactive steam.

The upper internals assembly includes an upper core barrel arranged intandem with the lower core barrel of the reactor. The ceiling of theupper core barrel is formed from an upper support plate. The peripheraledge of this support plate is seated around the upper edge of the uppercore barrel. Both the support plate and the upper core plate whichunderlies it include a plurality of apertures for both conducting thestream of hot, pressurized water exiting the fuel rod assemblies to theheat exchangers, as well as for conducting control rod assemblies.Separate guide tubes are provided between apertures in both the supportand core barrel plates which are aligned with each other and with one ofthe fuel assemblies in the lower core barrel. The purpose of these guidetubes is to align and guide the relatively long and flexible rodlets ofthe control rod assemblies into a particular fuel assembly.

The rate of the fission reaction taking place within the fuel rodassemblies is regulated by means of the control rod assemblies. Each ofthese control rod assemblies is formed from an array of stainless steeltubes containing a neutron absorbing substance, such as silver, indiumor cadmium. The stainless steel tubes (known as "rodlets" in the art)are suspended from a spider-like bracket. A reciprocable drive rod isconnected to the spider-like bracket for either inserting or withdrawingthe rodlets of the control rod assembly deeper into or farther out ofeach of the fuel rod assemblies in order to modulate the amount of heatgenerated thereby. These reciprocable drive rods are driven by controlrod drive mechanisms which may be of the electromagnetic linear motiondrive type devices or hydraulic drive type devices which move thecontrol rods in incremental steps into and out of the reactor core. Eachof the control rod drive mechanisms are attached to the reactor vesselhead by way of adapter tubes, with the control rod drive mechanism beingsealed to the adapter tube by way of an omega-type seal (so-calledbecause of its resemblance in cross-section to the Greek letter omega).

Because hot, radioactive primary water is contained within the controlrod drive mechanism, a leak may develop during the course of operationbetween the control rod drive mechanism and the adapter tube due tocorrosion. Any such leak will promote further corrosion and lead togreater contamination around the area of the leak due to the radioactivesteam released by the leak. Presently, due to the high radiation fieldand lack of working space, the omega seals must be repaired manuallywhich requires a shut down of the reactor vessel and the removal of thecontrol rod guide mechanism.

Applicant has observed that the servicing of broken omega seals requiresextensive down time of the reactor vessel, with a large amount of laborcosts as well as exposure of servicing personnel to potentially harmfulradiation. Clearly, there is a pressing need for a system for bothefficiently and effectively servicing broken omega seals that minimizesor eliminates reactor vessel down time, which typically costs theutility over $100,000 per day in lost revenues. Ideally, the systemshould reduce service personnel exposure to radiation contamination andcontain the radioactive steam emitted from the broken omega seal.

SUMMARY OF THE INVENTION

Generally speaking, the present invention is a system for remotelysecuring a canopy seal about the omega seal site so as to contain anyleakage that might occur between the control rod drive mechanism and theadapter tube. The system includes a stalk measuring device for initiallymeasuring the diameter of the reactor stalk head or adapter tube, asplit canopy installation fixture which is adjusted according to themeasurement detected by the stalk measuring device to position atwo-piece canopy seal about the omega seal site, and a robotic weld armfor performing both upper and lower radial welds about the canopy sealas well as C-shaped vertical welds between the two-piece canopy seal.

Because each adapter tube may vary slightly in diameter, and the canopyseal must mate with the adapter tube, the diameter of the adapter tubeis initially determined by the stalk measuring tool. This tool isanchored to a carousel mounted above the control rod drive mechanism andlowered below the lower end of the control rod drive mechanism to theomega seal site. The stalk measuring tool includes a pair of caliperarms which are initially calibrated to a predetermined diameter Once themeasuring tool is lowered to the omega seal site, the previouslycalibrated arms are moved into contact with the adapter tube with thedisplacement of the arms being detected by sensors that direct thisdetection to a control center which provides a digital readout of theactual diameter of the particular adapter tube. Once the actual diameterhas been detected, the stalk measuring tool is disengaged and removed.

The split canopy installation fixture is then adjusted to accommodatethe canopy seal and to properly engage the adapter tube in order to holdthe canopy seal in place for welding. The split canopy installationfixture cradling the canopy seal is then lowered to the omega seal sitewhere hydraulic cylinders are remotely activated to clamp theinstallation fixture about the adapter tube and to camlock the fixturein place. Once the fixture is camlocked in place, additional hydrauliccylinders are remotely activated to properly position the canopy sealabout the omega seal site. This fixture remains in place while therobotic weld arm descends to the omega seal site and temporarily tacksthe canopy seal in place. Once the canopy seal has been sufficientlysecured in place, the installation fixture is removed to allow therobotic weld arm total access to the canopy seal to complete the weldingprocess.

The robotic weld arm is provided with five degrees of freedom to allowthe robotic weld arm the flexibility and ability to work in a confinedarea. The arm is capable of performing the C-shaped vertical weldsbetween the two canopy seal halves as well as the radial welds about theupper and lower periphery of the canopy seal. The robotic weld arm isalso attached to the carousel positioned about an upper portion of thecontrol rod drive mechanism which provides for the robotic weld armsorbital movement about the control rod drive mechanism and the adaptertube. An extension tube controls the vertical movement of the roboticweld arm while magnetic induction motors control elbow and wrist jointsof the weld arm.

The weld process is viewed by two cameras located adjacent the torch cupof the robotic weld arm. One camera examines the leading edge of theweld while the other inspects the trailing edge of the weld.Additionally, in order to evacuate all of the oxygen encased by thecanopy seal, an argon gas purge opening is inserted under the canopyseal after the installation fixture has been removed. The weld arm thenperforms its predetermined welding sequence, welding the argon purgeopening last.

By providing the above mentioned canopy seal welding system, leakagesexperience at the omega seal site can be repaired from a position remotefrom the leakage site. This system will provide both efficient andeffective servicing of ruptured omega seals while minimizing, and inmost cases, eliminating reactor vessel down time, and significantlyreducing the radiation exposure of service personnel.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an elevational view of a nuclear reactor internals partiallyin section to which the present invention is adapted.

FIG. 2 is a cross-sectional exploded view cf area A of FIG. 1 with acanopy seal in place.

FIG. 3 is an elevational view of the stalk measuring device inaccordance with a preferred embodiment of the present invention.

FIG. 4 is a side view of the stalk measuring device illustrated in FIG.3.

FIG. 5 is an elevational view of the split canopy installation fixturein accordance with a preferred embodiment of the present invention.

FIG. 6 is partial side view of the split canopy installation fixture ofFIG. 5.

FIG. 7 is a top view of the split canopy installation fixture of FIG. 5.

FIG. 8 is a partial section elevational view of the robotic weld arm inaccordance with a preferred embodiment of the present invention.

FIG. 9 is a side view of the robotic weld arm illustrated in FIG. 8.

FIG. 10 is a cross-sectional view of the drive mechanism for the wristjoint of the robotic weld arm taken along line W--W of FIG. 9.

FIG. 11 is a partial cross-sectional view of the weld wire feedmechanism taken along line S--S of FIG. 8.

FIG. 12 is a top view of the carousel in accordance with a preferredembodiment of the present invention.

FIG. 13 is a cross-sectional elevational view of the carouselillustrated in FIG. 12 taken along line X--X.

FIG. 14 is a partial sectional view of the carousel illustrated in FIG.12 taken along line Z--Z.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring to the drawings, and particularly to FIG. 1, the reactor 1shown therein comprises a pressure vessel 2 having a removable closurehead 4 attached to the pressure vessel 2 by a plurality of bolts (notshown). The pressure vessel 2 may be of a well known type suitable forcontaining a fluid coolant at a relatively high pressure. In the presentcase the coolant utilized is water; however, other suitable fluids maybe utilized as a coolant if desired. The pressure vessel 2 has an inletnozzle 6 and outlet nozzle 8. The coolant is circulated through thereactor vessel in a manner well known in the art. Fuel assemblies 10 aremounted within the pressure vessel 2 between a lower core plate 12 andan upper core plate 14 which constitutes the reactor core. The lowercore plate 12 is attached by welding to a core barrel 16 having an upperflange 18 which rest on a ledge 20 of the pressure vessel 2. The uppercore plate 14 is supported from a deep-beamed upper support plate 22 bymeans of a plurality of support tubes 24.

The reactor is provided with control rod drive mechanisms 26 that may beof any conventional type including electromagnetic linear motion drivetype devices or hydraulic drive type devices which move the control rodsin incremental steps into and out of the reactor core. As was notedpreviously, of the control rod drive mechanisms 26 are attached to theclosure head 4 by way of adapter tubes 28 with the control rod drivemechanism 26 being sealed to a respective adapter tube 28 by way of anomega seal 30 as shown in FIG. 2.

As can be seen from FIG. 2 the omega seal 30 is the original sealbetween the adapter tube 28 and the control rod drive mechanism 26.Further, as can be noted from FIG. 2, a canopy seal 32 having asemi-circular cross-section is positioned and secured so as to enclosethe entire periphery of the omega seal 30. It is the proper positioningand securing of a canopy seal 32 which constitutes the preferredembodiment of the present invention.

Generally speaking, the process of welding the canopy seal 32 in placeabout the omega seal 30 is done remotely by means of a control rod drivecanopy seal weld head illustrated in FIGS. 8 and 9 of the drawings.Canopy seal 32 is sealed about the omega seal 30 in order to contain anyleakage at the omega seal site. The control rod drive mechanism canopyseal weld system is composed of three individual tools each performing aparticular function with the primary goal of being to remotely weld thecanopy seal 32 to contain any leakage at the omega seal site. The threecomponent tools are a stalk measuring device 34 shown in FIGS. 3 and 4,a split canopy installation fixture 36 shown in FIGS. 5, 6 and 7 and arobotic weld arm 108 shown in FIGS. 8 and 9. Additionally, a carouselfor positioning and maneuvering the stalk measuring device 34 and therobotic weld arm 108 is illustrated in FIGS. 12, 13 and 14. Theseindividual devices are used in conjunction with one another in order toproperly position and weld the canopy seal 32 about the omega seal site.

The stalk measuring device 34 is used initially to determine the precisediameter of the adapter tube 28 such that the split canopy installationfixture 36 may properly position the canopy seal 32 about the omega sealsite. Once the diameter of the adapter tube 28 is determined,adjustments can be made to the split canopy seal installation fixture 36so that this fixture will properly engage the adapter tube 28 in orderto hold the canopy seal in its proper position for welding. The stalkmeasuring device 34 is anchored to the carousel 38 by any conventionalmeans; however, because the stalk measuring device 34 is onlytemporarily mounted to the carousel 38 it is preferred that a matingdovetail structure 40 be utilized. Mounted to the dovetail structure 40is an extension beam 42 to which an air cylinder 44 is pivotallysecured. The air cylinder 44 is pivotally mounted within bracket 46 byway of pivot 48. The extension and retraction of the air cylinder 44 iscontrolled by compressed air which is fed to, and exhausted from the aircylinder 44 through tube fittings 50 and 51. Pivotally mounted to theextension beam 42, through pivot shaft 52, is a caliper supportstructure 54, with the caliper support structure 54 being adapted to bedisplaced in an angular direction by the air cylinder 44. The aircylinder 44 is further pivotally attached to the caliper supportstructure through pivot 56, this pivotal action to be described ingreater detail hereinafter. The caliper support structure 54 supports anair cylinder 58 which is provided between a pair of caliper arms 60 and62. A plate 64 is provided to extend from the rearward end of thecaliper arm 62 and is contacted by a displacement sensor 66. The outputgenerated by the displacement sensor 66 is forwarded to a control center(not shown) by way of cable 68 whereby any movement of the caliper arm62 is transmitted to the control center which digitally displays theresultant displacement.

The caliper arms 60 and 62 are initially calibrated to a knownpredetermined diameter prior the positioning of the stalk measuringdevice 34 adjacent the control rod drive mechanism 26. The stalkmeasuring device 34 is then anchored to the carousel 38 and lowered downthe housing of the control rod drive mechanism 26 to a position adjacentthe adapter tube 28. By actuation of the air cylinder 44, the calipersupport structure 54 is pivoted to a position normal to the extensionbeam 42. In doing so, the caliper arms 60 and 62 will be positionedadjacent diametrically opposed sides of the adapter tube 28. Once thestalk measuring device 34 has reached this position the air cylinder 58is actuated in order to draw the caliper arms 60 and 62 towards oneanother. This displacement is sensed by the sensor 66 through contactwith the plate 64 with the data being forwarded to the control centerwhich provides a digital read out of the actual diameter of the adaptertube 28. Once this actual diameter of the adapter tube 28 has beendetermined, the air cylinder 58 reverses the action on the caliper arms60 and 62 which move away from one another. The air cylinder 44 thenretracts in order to return the caliper support structure 54 to itsoriginal position. Once this position is reached, the stalk measuringdevice 34 is disconnected from the carousel 38 and removed. As mentionedpreviously, this measurement is used to properly adjust the split canopyinstallation fixture 36 in order to properly position the installationfixture 36 about the adapter tube 28.

Turning now to FIGS. 5, 6 and 7, the split canopy installation fixture36 will be discussed in greater detail. As can be seen from FIGS. 6 and7, the split canopy installation fixture 36 includes a pair ofsemi-circular buckets 70 and 72 for accommodating the two piece canopyseal 32. Each of the buckets 70 and 72 includes a plurality of canopyseal retaining clips 74 which aid in maintaining the canopy seal 32 inposition within the buckets 70 and 72 during their positioning. Each ofthe buckets 70 and 72 are reciprocably mounted on elevating aircylinders 76 for elevating the buckets 70 and 72 for properlypositioning the canopy seal beneath the control rod drive mechanism 26.Each of the elevating air cylinders are mounted to the two-piece adaptertube clamp 78a and 78b which are hingedly connected to one another byway of hinge 80. The hinge 80 is pivotable about the pivot pin 82 suchthat the two-piece adapter tube clamp 78a, 78b may be opened andpositioned about the adapter tube 28 and subsequently closed andcamlocked tightly to the adapter tube 28. An air cylinder 84 which ispivotally mounted to one of the elevating air cylinders 76 by way ofbracket 86 and pin 88 is provided for displacing the hinge 80 in orderto open and close the two-piece adapter tube clamp 78a, 78b along thesplit line 90. An additional dual air cylinder construction is furtherpivotally mounted to the same elevating air cylinder as that of aircylinder 84. The dual air cylinder consist of a first air cylinder 92which is pivotally secured to the elevating air cylinder 76 and a secondair cylinder 94 which is pivotally mounted at a first end to the firstair cylinder 92 by way of pivot pin 96 and is pivotally mounted at asecond end to a hinge 98 and a lever arm 100. The hinge 98 includes acamlock 102 which may be forced about the lock lug 104 in order tofixedly clamp the two-piece adapter tube clamp 78a, 78b about theadapter tube 28. In order to maneuver the split canopy installationfixture 36 to a position below control rod drive mechanism 26 andadjacent to the adapter tube 28, lift flanges 106 are provided andsecured to a respective one of the buckets 70 and 72. These flangesallow the split canopy installation fixture 36 to be lowered by way of arope or pole to the desired position.

The purpose of the split canopy installation fixture 36 is to transportthe two-piece canopy seal 32 to the omega seal site and properlyposition the canopy seal 32 about the adapter tube 28. The split canopyinstallation fixture 36 and the canopy seal 32 are lowered to a positionadjacent the adapter tube 28 by using ropes or a pole connected to thelift flanges 106. The two halves of the canopy seal rest in the buckets70 and 72 as the fixture 36 is lowered. While not shown in the figures,each half of the canopy seal includes locator pins while each of thebuckets 70 and 72 include pin holes for accommodating the locator pinsof the canopy seal 32 in order to maintain the canopy seal 32 in placeduring the lowering of the split canopy installation fixture 32.

Once in a position adjacent the adapter tube 28, air cylinder 84 isactivated so as to close the two-piece adapter tube clamp 78a and 78babout the adapter tube 28. Once the two-piece adapter tube clamp hasbeen closed around the adapter tube 28, the first air cylinder 92 isactivated in order to pivot the hinge 98 to an initial position aboutthe lock lug 104. After this position is reached, the second aircylinder 94 is actuated in order to further push the camlock 102 over alock lug 104 and firmly secure the adapter tube clamp 78a, 78b to theadapter tube 28. Upon completion of the clamping process, the elevatingair cylinders 76 are actuated in unison so as to elevate the canopy seal32 to the proper position below the control rod drive mechanism 26. Thecanopy seal 32 is then held in place while the robotic weld arm 108, tobe discussed in greater detail below, descends and temporarily tacks theseal in this position. Once the canopy seal 32 has been properly tacked,the buckets 70 and 72 of the installation fixture 36 are lowered and thecamlock 102 is released so that the installation fixture 36 may beremoved. Removal of the installation fixture 36 facilitates the roboticweld arm's access to all necessary weld areas of the canopy seal 32.

The robotic weld arm 108 is illustrated in detail in FIGS. 8 and 9. Therobotic weld arm 108 includes an upper housing 110, an intermediatehousing 112 and a lower housing 114 The upper housing 110 accommodates afirst magnetic induction motor 116 which when actuated rotates gear 118which is meshed with gear 120 which is capable of rotating theintermediate housing 112 about an elbow axis 122 in a desired direction.The upper housing 110 further accommodates the weld wire spool mountbracket 124 which is secured to the upper housing 110 by bolts 126. Thespool mount bracket 124 carries a pair of weld wire spools 128 with thewire from a first spool being used for the vertical C-shaped weldsbetween the two-piece canopy seal structure and the weld wire of asecond spool being used to perform the upper and lower radial weldsabout the canopy seal 32.

A weld wire drive mechanism 130 is secured to the intermediate housing112. The weld wire drive mechanism 130 includes a pair of wire feeddrive motors 132 and 134 which rotate the drive shafts 133 and 135respectively. As shown in FIG. 11, each of the drive shafts 133 and 135drive respective wire feed drive rollers 136 and 138 which drive theweld wires 137 and 139. Counter wire feed rollers 140 and 142 areprovided for pressing the respective weld wire against the driverollers. The force in which the counter rollers 140 and 142 contact theweld wire may be readily adjusted by the tension adjustment screws 141and 143. Springs 144 and 146 assure the continuous contact between thecounter rollers 140 and 142 and the respective weld wire. As can befurther noted from FIG. 11, wire feed guide tubes 145 and 147 areprovided in order to guide the weld wire through the weld wire drivemechanism 130 to the weld head 148.

Intermediate housing 112 further accommodates a second magneticinduction motor 150 as shown in FIG. 10. The second magnetic inductormotor 150 includes a drive shaft 152 which drives gear 154 which mateswith gear 156 which rotates the shaft 158 and subsequently the gear 160mounted within the gear housing 162. Gear 160 is meshed with acooperating gear 164 within the gear housing 162 which rotates the shaft166 within the bearings 168 which ultimately pivots the lower housing114 about a wrist axis which is constituted by the shaft 166.

Cameras 170 and 172 are provided for inspecting both the leading andtrailing edges of the weld as it is being formed by the weld head 148.The weld head 148 includes a gas torch 174 and a tungsten weld wire wire176. An additional weld wire guide 178 is provided at a position nearthe end portion of the weld head 148 so as to appropriately guide theweld wire to a position adjacent the weld head 148. The cameras 170 and172 are additionally provided with lens covers 180 for protecting thecameras during the welding process.

The robotic weld arm 108 is provided with five degrees of freedom, onebeing the rotation about the wrist axis, the second being the rotationabout the elbow axis 122. A third degree of movement is the verticalmovement of the weld head 148 which is performed by piston cylinderassembly 182 which is accommodated in the lower housing 114. The pistoncylinder assembly 182 is composed of a piston 184 having a shaft 186secured to the weld head 148. Hydraulic fluid is provided to the pistoncylinder assembly through the hydraulic fittings 187 and 188. By varyingthe flow of fluid through the hydraulic fittings 187 and 188, thevertical positioning of the weld head may be varied. This feature willbe discussed in greater detail hereinafter.

Two additional degrees of freedom are provided to the robotic weld arm108 by way of the carousel 38 shown in FIGS. 12-14. The carousel 38 isadapted to be positioned about an upper portion of the control rod drivemechanism 26. As shown in FIG. 13 the carousel 38 includes a chuckhousing 192 and an inner housing 194 with the chuck housing including areciprocable resilient pad 196 which may be readily displaced by the pin198. Once the carousel 38 is positioned about the control rod drivemechanism 26, the pin 198 is driven forwardly so as to displace andpress the resilient pad 196 against an upper portion of the control roddrive mechanism 26. This will maintain the carousel in a stable positionrelative to the control rod drive mechanism 26. A magnetic inductionmotor 200 is supported on a top hat plate 202 above the inner housing194. The magnetic induction motor 200 includes a drive shaft 204 havinga gear 206 fixedly secured thereto. The gear 206 is meshed with a ringgear 208 which is secured to an outer housing 210 by way of a flange212. The outer housing 210 is permitted to rotate about the innerhousing 194 by way of bearings 214.

As can be seen from FIGS. 12 and 14, a mount 216 is fixedly secured toan outer portion of the outer housing 210 which supports the roboticweld arm 108 as well as a mechanism for vertically displacing therobotic weld arm. As shown in FIG. 14, the mount 216 is secured to theouter housing 210 by way of bolts 218, and accommodates a magneticinduction motor 220. A telescopic tubular construction 222 is suspendedfrom the mount 216 and includes an outer tubular member 224 and an innerdisplaceable tubular member 226. As noted in FIG. 8, this inner tubularmember 226 is also attached to the robotic weld arm and surrounds thescrew shaft 228. The screw shaft 228 is connected to the output driveshaft 230 of the magnetic induction motor 220. Rotation of the outputdrive shaft 230 and consequently the rotation of the screw shaft 228causes of the displacement of the inner tubular member 226 relative tothe outer tubular member 224 which subsequently results in the verticaldisplacement of robotic weld arm 108. Additionally, mounted to an outerportion of the outer tubular member 224 is a spacer which includesrollers 234 and 235 which contact an outer portion of the control roddrive mechanism 26 so as to aid in the stabilization of the robotic weldarm 108.

As can be seen from the foregoing, it is the carousel 190 in conjunctionwith the robotic weld arm 108 which provides the necessary five degreesof freedom such that the robotic weld arm 108 can perform both the upperand lower radial welds as well as the C-shape vertical welds in anarrowly confined space.

The motion of the robotic weld arm is controlled by a central computersystem which has been programmed with preset data for controlling thepositioning of the robotic weld arm 108 as well as the speed of thewelding process. The welding process is controlled by an ARC machine(not shown) the ARC machine provides the necessary power to the roboticarm for performing the welding process The central computer whichcontrols the positioning of the robotic weld arm also controls thepositioning of the torch and the speed of the torch movement. As notedpreviously, the weld head 148 may be manipulated in a direction parallelto the direction in which the weld head 148 is positioned by the wristaxis by way of the piston cylinder assembly 182. This allows for aninstantaneous movement of the tungsten weld wire 176 so as to maintain aconstant ARC between the tungsten weld wire 176 and the surface beingwelded.

The entire welding process is carried in the following manner.Initially, the carousel 38 is positioned about the control rod drivemechanism 26 and secured thereto by the resilient pad 196. Once in thisposition, the stalk measuring device 34 can be secured thereto andsuspended adjacent the control rod drive mechanism 26 and the adaptertube 28. Upon actuation of the air cylinder 44, the caliper supportstructure will pivot and position the caliper arms 60 and 62 ondiametrically opposite sides of the adapter tube 28. Air cylinder 58 isthen actuated to displace the caliper arms 60 and 62 towards one anotherwith this displacement being sensed by the displacement sensor 66. Thedisplacement sensed by the sensor 66 is transmitted by way of the cable68 to a control center where the actual diameter of the adapter tube 28is provided. Once the actual diameter of the adapter tube 28 has beendetermined, the stalk measuring device 34 is removed from its positionadjacent control rod drive mechanism 26.

The split canopy installation fixture 36 is then adjusted such that itmay be securely fixed to the adapter tube 28. The two-piece canopy sealis next positioned within the buckets 70 and 72 of the split canopyinstallation fixture 36 with this fixture then being lowered to aposition adjacent the adapter tube 28. Next, the hydraulic air cylinder84 is activated such that the hinge 80 is displaced to open thetwo-piece adapter tube clamp 78a, 78b. The split canopy installationfixture is then positioned about the adapter tube 28 with the aircylinder 84 then being actuated in a reverse manner to close thetwo-piece adapter tube clamp 78a, 78b about the adapter tube 28. Oncethe installation fixture 36 is closed around the adapter tube, it iscamlocked in place by the cooperating movement of the first and secondair cylinders 92 and 94 which positions the camlock 102 about the locklug 104. After the fixture has been secured about the adapter tube 28,the elevating air cylinders 76 are actuated so as raise the buckets 70and 72 to properly position the canopy seal 32 as shown in FIG. 2. Thecanopy seal is held in place by the split canopy installation fixture 36while the robotic weld arm 108 descends to a position adjacent the sealand temporarily tacks the canopy seal in place. When the canopy seal 32has been properly tacked in place, the buckets 70 and 72 of theinstallation fixture 36 are retracked, the camlock is released and thefixture is removed. Removal of the split canopy installation fixture 36facilitates the robotic weld arm's access to all necessary weld areas ofthe canopy seal 32. The robotic weld arm 108 with its previouslymentioned five degrees of freedom is capable of following the C-shapedvertical welds between the two-piece canopy seal as well as the upperand lower radial welds in the confined space between adjacent controlrod drive mechanisms 26.

After the split canopy installation fixture 36 has been removed, anargon gas purge is inserted in the canopy seal 28 to a evacuate anyoxygen at the omega seal site. The preset data contained in the controlcenter directs the robotic weld arm 108 to complete an initial tackingof the seal in place. The robotic weld arm 108 then begins the verticalC-shape welds and subsequently completes the top and bottom radial weldsexcept for a vent opening which is provided for the purge gas insertion.The purge gas insertion is then removed and the robotic weld arm appliesa final hot pass weld which closes the argon gas purge vent opening. Asstated previously, the welding process is controlled by an ARC machinewhich provides the necessary power to the robotic weld arm 108 forwelding. During the welding process data is continuously presented tothe control center which is used to manipulate the robotic weld arm 108and particularly the tungsten weld wire 176.

I claim:
 1. In a system for remotely welding a canopy seal about aruptured seal site between a control rod drive mechanism and an adaptertube of a nuclear reactor vessel, a robotic weld arm comprising;anelongated housing having an upper portion, an intermediate portion and alower portion with a first end of said intermediate portion beingpivotally connected to a lower end of said upper portion with respect tosaid lower portion, and a second end of said intermediate portion beingpivotally connected to an upper end of said lower portion with respectto said upper portion; a welding means translationally mounted withinsaid lower portion for welding said canopy seal about said ruptured sealsite; and translational movement means for imparting translationalmovement to said welding means relative to a direction of said lowerportion of said housing; wherein said welding means and the motion ofsaid robotic weld arm are remotely controlled by a preprogrammed controlmeans.
 2. The robotic weld arm as defined in claim 1, further comprisinga weld wire feed means for feeding weld wire to said welding meansduring the welding process.
 3. The robotic weld arm as defined in claim2, wherein said weld wire feed means further comprises a driven feedroller for feeding said weld wire, and a cooperating counter roller formaintaining said weld wire in contact with said weld wire feed roller.4. The robotic weld arm as defined in claim 3, wherein said driven feedroller is driven by a magnetic induction motor.
 5. The robotic weld armas defined in claim 2, wherein said weld wire feed means is a dual weldwire feed means for selectively feeding either one of two weld wires tosaid welding means.
 6. The robotic weld arm as defined in claim 1.further comprising a first pivoting means for pivoting said intermediateportion of said housing relative to said upper portion.
 7. The roboticweld arm as defined in claim
 6. wherein said first pivoting meansincludes a drive means for selectively rotating a drive shaft, a firstgear concentrically mounted in a fixed position on said drive shaft, anda second gear fixedly mounted with respect to said intermediate portionand meshed with said first gear, so that rotation of said drive meanspivots said intermediate portion with respect to said upper portion. 8.The robotic weld arm as defined in claim 1, further comprising a secondpivoting means for pivoting said lower portion relative to saidintermediate portion.
 9. The robotic weld arm as defined in claim 8,wherein said second pivoting means includes a drive means forselectively rotating a drive shaft, a first gear concentrically mountedin a fixed position on said drive shaft, a second gear meshed with saidfirst gear and fixed to a first concentric transfer shaft fortransferring rotational movement to a third gear concentrically mountedon said first transfer shaft, and a fourth gear meshed with said thirdgear and concentrically mounted on a second transfer shaft, so that saidlower portion of said housing is fixed to said second transfer shaft androtation of said drive shaft is transferred into pivotal movement ofsaid lower portion.
 10. The robotic weld arm as defined in claim 1.wherein said translational movement means includes a piston cylinderassembly having a displaceable shaft connected to said welding means forselectively moving said welding means toward and away from a weldingsurface.
 11. The robotic weld arm as defined in claim 1, furthercomprising at least one camera for viewing the weld during the weldingprocess.
 12. The robotic weld arm as defined in claim 11, wherein twocameras are provided with a first camera viewing a leading edge of saidweld and a second camera for viewing a trailing edge of said weld. 13.The robotic weld arm as defined in claim 1, wherein said welding meansis controlled by an ARC machine.
 14. The robotic weld arm as defined inclaim 1, further comprising a telescopic positioning means connected toan upper end of said upper portion for extending and retracting saidrobotic weld arm in a direction of said upper portion.
 15. The roboticweld arm as defined in claim 14, wherein said telescopic positioningmeans includes an outer tubular section, an inner tubular housing, ascrew shaft extending in a longitudinal direction of said telescopicpositioning means within said tubular sections, means for rotating saidscrew shaft, and a translational means fixedly mounted within said innertubular housing and cooperating with said screw shaft such that rotationof said screw shaft extends and retracts said inner tubular housingrelative to said outer tubular housing thereby extending and retractingsaid robotic weld arm.
 16. The robotic weld arm as defined in claim 15,further comprising an orbital motion means having an inner portionfixedly secured to one of said tubular members and an outer portionrotatably positioned about said inner portion, wherein said means forrotating said screw shaft and said outer tubular section are fixedlysecured to said orbital motion means, and rotation of said outer portionof said orbital motion means transmits orbital rotation to said roboticweld arm about said tubular members.